Doxy-PEP: Prevent STIs After Sex

Studies show Doxy-PEP cuts your risk of chlamydia by up to 89%, syphilis by up to 87%, and gonorrhea by about 55%. These numbers come from three large clinical trials and are backed by the CDC. Important note: These results are based on studies in men who have sex with men (MSM) and transgender women. Results may differ for other groups — see our questions about cisgender women and heterosexual men below.

Take 2 pills (200mg total) as soon as you can after sex without a condom. The sooner the better — ideally within 24 hours, but it still works if taken within 72 hours. Important: Don't take more than 200mg in any 24-hour period, even if you have sex multiple times.

No. Doxy-PEP only works against bacterial infections like chlamydia, gonorrhea, and syphilis. It does NOT protect against HIV, Hepatitis B, HPV, or herpes. If you want HIV protection, ask about HIV PrEP — and condoms still offer the broadest protection.

The most common side effects are sun sensitivity (wear sunscreen!), upset stomach, and throat irritation. To avoid problems: take it with food and a full glass of water. Also, don't take it within 2 hours of dairy, antacids, or calcium/iron/magnesium supplements — these can stop the medication from working properly.

Yes. Doxy-PEP lowers your risk but isn't 100% effective. You should still get tested every 3-6 months. We include a lab requisition with your consultation so you can get tested whenever you're ready.

The consultation ($49 every 3 months or $69 one-time) isn't covered by provincial health insurance, but the medication itself is a cheap generic drug. Your private insurance might cover it, and if you're under 25 in Ontario, OHIP+ may cover the medication cost. Ask your pharmacy for exact pricing.

Most adults can use it. You shouldn't take Doxy-PEP if you're allergic to this medication or other tetracycline antibiotics, or if you're pregnant or breastfeeding. The strongest evidence for effectiveness is in men who have sex with men (MSM) and transgender women — see our FAQs below about cisgender women and heterosexual men.

We do prescribe Doxy-PEP to cisgender women, but here's what you should know about the evidence:

The research so far: The studies showing 87-89% effectiveness were done mostly in men who have sex with men (MSM) and transgender women. One study in cisgender women in Kenya didn't show a benefit — but researchers don't consider this proof that it doesn't work, because of major problems with the study.

The main problem? People didn't actually take the pills. Participants said they took doxycycline after sex, but when researchers tested their hair, only about 30-40% actually had the drug in their system. So the study mostly tested whether people remembered to take the pill — not whether the pill actually works.

There may be biological differences too. Some researchers think the medication might not reach the same levels in vaginal tissue as it does in rectal tissue, or might clear out faster. The timing rules (take within 72 hours) were figured out based on rectal exposure, not vaginal.

Bottom line: Until we have better data for cisgender women, the 87-89% success rates might not apply to vaginal sex. More studies are happening now. If you're interested, our clinician can walk you through what we know and help you decide.

The honest answer: we don't know. There are no studies that have directly tested Doxy-PEP in heterosexual men having vaginal sex.

What the guidelines say: The CDC (2024) recommends Doxy-PEP only for men who have sex with men (MSM) and transgender women who've had a bacterial STI in the past year. For heterosexual men, the CDC says "no recommendation can be given at this time" — not because it's proven useless, but because there simply isn't enough research.

Would it likely work? Maybe. Doxycycline reaches good levels in penile/urethral tissue and is already used to treat chlamydia and syphilis. So there's no obvious reason it wouldn't help prevent these infections. However:

• Chlamydia & syphilis: There may be benefit, but it's unproven
• Gonorrhea: Likely limited benefit — in Canada, over 70% of gonorrhea samples from heterosexual men are resistant to at least one antibiotic, and resistance to tetracyclines (like doxycycline) is common

Our approach: We can prescribe Doxy-PEP to heterosexual men, but we're upfront that this is off-label use based on data from other groups. We'll discuss the potential benefits, the unknowns, and antibiotic resistance concerns so you can make an informed choice. If you have recurring STIs or high-risk exposures, our clinician can help you weigh the options.

Bottom line: Any benefit for heterosexual men is theoretical, not proven. Major guidelines don't recommend it routinely for this group — but that doesn't mean it definitely won't help.

Each prescription gives you enough pills for 3 uses (600mg total). Need more? Join our Prescription Renewal Program for $49 every 3 months. One renewal per 3-month period is included. A one-time renewal is $69.

Nope — testing is optional. You don't need to get tested to get a prescription. That said, we include a lab requisition with your consultation at no extra cost, so you can get tested whenever you want. We do recommend getting tested every 3-6 months if you're sexually active.

This is a fair concern. Here's the thinking: the CDC and other health experts still recommend Doxy-PEP because preventing STIs now outweighs the possible future risk of resistance. Unlike taking antibiotics every day, Doxy-PEP is only taken when you need it — maybe just 2-3 times a month for most people. That limits how much antibiotic you're exposed to. So far, studies haven't shown major resistance problems in Doxy-PEP users, but research is ongoing.

No — it only works after. The "PEP" stands for "post-exposure prophylaxis," meaning you take it after sex, not before. Taking it beforehand hasn't been studied and isn't recommended. All the research showing it works was based on taking it within 24-72 hours after sex.

Intakes submitted during business hours (9 AM - 9 PM ET) are reviewed the same day. After-hours submissions are reviewed the next business day. Most prescriptions are reviewed and approved the same day - 90% are reviewed within 90 minutes.